Spray Pyrolysis Technique Enables Uniform Precursor Layer for Large-Area Flexible CZTSSe Solar Cells

Kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) is a promising candidate for sustainable photovoltaics, realizing high efficiency via low-cost fabrication methods remains a challenge due to the difficulty of defect passivation. Herein, we report a feasible approach for fabricating high-quality CZTSSe absorber using the spray pyrolysis technique. Through optimizing the effects of spray flow rate and substrate temperature, we establish a critical processing window that ensures the formation of a dense, void-free precursor layer. The optimized absorber exhibits superior crystallinity with significantly reduced surface roughness, facilitating a high-quality interface with the CdS buffer layer. Deep-level defect analysis reveals that this optimized crystallization path can effectively suppress Cu/Zn cation disorder and minimize band-tail states, yielding a low Urbach energy of 33.98 meV. Consequently, the non-radiative recombination is substantially mitigated, accompanied by a reduced interface trap density and lower defect activation energy. The optimized CZTSSe solar cell achieves a PCE of 9.53% (active area: 0.21 cm²), accompanied by an enhanced open-circuit voltage. Furthermore, a large-area flexible CZTSSe solar cell with an active area of 1.22 cm² achieves a PCE of 7.65% and retains 91.2% of its initial efficiency after 4 000 bending cycles. This work presents a straightforward and scalable approach for developing large-area kesterite solar cells.